A trackball device detects the rotating direction and speed of a ball (sphere) rotated by a user with a pair of orthogonally arranged encoders respectively corresponding to the X- and Y-axis directions, and operates the cursor (pointer) displayed on a screen in accordance with the detected rotating direction and speed. Such a trackball is widely used as the interface unit of a computer typified by a personal computer, a medical image diagnostic apparatus typified by an ultrasonic diagnostic apparatus, and the like.
FIG. 17 is a side view of a trackball device 80 used for an operation panel 90 of a conventional ultrasonic diagnostic apparatus. FIG. 18 is a sectional view of the trackball device 80 shown in FIG. 17. As shown in FIGS. 17 and 18, the conventional trackball device 80 includes a ball 81, a casing 82 having an opening portion to expose part of the ball 81, and a dial 83 used either for operation in an axial direction different from that indicated by the trackball or for control of application software of the ultrasonic diagnostic apparatus. The ball 81 is housed in the casing 82 while being partially exposed from the opening portion and being rotatable. The dial 83 is provided along the opening portion. The user can operate the cursor or the like on the screen by rotating the ball 81 by manually operating the exposed portion of the ball 81 or rotating the dial 83 clockwise or counterclockwise.
In general, the ball 81 tends to become dirty because the user touches it, and dust easily stays in the ball housing portion of the casing 82. Jelly applied to a patient in ultrasonic diagnosis tends to adhere to the trackball device used in an ultrasonic diagnostic apparatus. Such dirt on the ball and dust and the like staying in the ball housing portion cause a deterioration in the detection capability of the trackball. Periodic maintenance and cleaning are therefore indispensable to this device.
However, the conventional trackball device has the following problems at the time of maintenance or cleaning. In order to remove the ball 81 from the ball housing portion of the casing 82, the upper plate of the operation panel 90 of the computer has to be detached, then the trackball device 80 has to be detached from the operation panel 90, and then the trackball device 80 has to be disassembled using specially-designed screws. Therefore, the maintenance or cleaning of the trackball device can be performed only by a professional and requires a great deal of time and labor. Since the user cannot clean the trackball device regularly, the cleaning of the ball and the removal of foreign matter from inside a hole or opening may be delayed. As a result, the detection performance of the trackball may be impaired, and the reliability of the apparatus incorporating the trackball may be deteriorated.
It is intended to provide a trackball device which does not have to be detached from an operation panel and does not have to be maintained or cleaned by a professional, and also to provide an ultrasonic diagnostic apparatus incorporating the trackball device.